Effect of Magnetic-Lattice Transformations on Low-Temperature Plasticity and Fracture of Chromium Single Crystals

Analysis of the literature indicates an interconnection of the lattice and magnetic subsystems of chromium, which suggests the further study of changes in low-temperature plasticity and fracture of chromium resulting from magneto-lattice transformations during thermal cycling in the range of 373 <-> 77 K. For the initial microalloyed Eu single crystals of Cr (the content of impurities C-i approximate to 10(-3) wt.%) with orientations [110] and [112] along the compression axes, a monotonous growth of the yield point was observed in the temperature range from room temperature to T = T-x approximate to 170 K (T-x is the temperature of cold-brittleness or the temperature of ductile-brittle transition). When the temperature was lowered in the range of T-x-4.2 K, the samples became brittle, with a decrease in the fracture stress, which is due to the growth of local stresses at the concentrators. As a result of thermal cycling accompanied by multiple phase transformations from the paramagnetic to the antiferromagnetic AF(1) and AF(2) states and vice versa, a decrease in the T-x value of chromium was observed of approximate to 20 K. The effect is related to the occurrence of relaxation processes near stress concentrators due to the displacement of the walls of domain structures and also cyclic striction deformations that compensate for the volume change caused by overheating and supercooling of the sample due to a rapid change in temperature. Published by AIP Publishing.